Rod Ejection Accident Research Articles

Realistic Scoping Study of Reactivity Insertion Accidents for Typical PWR and BWR Cores

The rod ejection accident in a pressurized water reactor and the control rod drop accident in a boiling water reactor are analyzed in this paper, both in a best-estimate (realistic) and a conservative manner. CORETRAN, a modern three-dimensional time-dependent nodal code, is used for all simulations. In all considered cases, the resulting peak fuel enthalpy is far less than the current licensing limit of 180 cal/g. The advantage of using a three-dimensional code over the classical point-kinetics approach can be summarized: The power peak is nominally a factor of 10 times lower, and the pulse is 10 times wider. Therefore, a three-dimensional approach predicts a much milder event. Sensitivity studies were performed to identify the influence of several parameters on the reactivity insertion simulations.

へん平二重炉心型高転換加圧水型原子炉の反応度異常事象に対する成立性

A conceptual design of a double-flat-core type high conversion pressurized water reactor (HCPWR) has been developed at the Japan Atomic Energy Research Institute to improve fuel utilization. In thermal-hydraulic feasibility studies of the proposed concept, major six events such as large and small break LOCAs have been analyzed with the best estimate code REFLA/TRAC. This paper describes the results of control rod ejection accident analyses as a part of the series of analyses. The calculations were performed according to the licensing analysis on current PWRs. The calculated results showed that the proposed concept had larger safety margines than current PWRs. Therefore, the proposed concept is considered to be feasible from a view point of safety analysis of control rod cruster ejection accident. It is seen that the large safety margine of the proposed concept is originated from smaller excess reactivity, smaller maximum linear heat generation rate and smaller rod worth per a control rod than those of current PWRs.

The implication of sensitivity analysis on the safety and delayed-neutron parameters for fast breeder reactors

The delayed-neutron energy spectra for LMFBRs are not as well known as those for LWRs. These spectra are necessary for kinetics calculations which play an important role in safety and accident analyses. A sensitivity analysis was performed to study the response of the reactor power and power density to uncertainties in the delayed-neutron spectra during a rod-ejection accident. The accidents studied were central control-rod ejections with ejection times of 2, 10 and 30s. A two-energy group and two-precursor group model was formulated for the International Nuclear Fuel Cycle Evaluation (INFCE) reference design MOX-fueled LMFBR. The sensitivity analysis is based on the use of adjoints so that it is not necessary to repeatedly solve the governing (kinetics) equations to obtain the sensitivity derivatives. This is of particular importance when large systems of equations are used. The power and power-density responses were found to be most sensitive to uncertainties in the spectrum of the second delayed-neutron precursor group, resulting from the fission of 238U, producing neutrons in the first energy group. It was found, for example, that for a rod-ejection time of 30 s, an uncertainty of 7.2% in the fast components of the spectra resulted in a 24% uncertainty in the predicted power and power density. These responses were recalculated by repeatedly solving the kinetics equations. The maximum discrepancy between the recalculated and the sensitivity analysis response was only 1.6%. The results of the sensitivity analysis indicate the need for improved delayed-neutron spectral data in order to reduce the uncertainties in accident analyses.

Application of Reactivity Weighting to Rod Ejection Accident Analysis in a Pressurized Water Reactor

Application of Reactivity Weighting to Rod Ejection Accident Analysis in a Pressurized Water Reactor

On the Use of Point Kinetics for the Analysis of Rod-Ejection Accidents

The results of a numerical study as to the adequacy of the point kinetics method for analyzing rod-ejection accidents are presented. Two-group slab representations of three different seed-blanket r...